Graphene is a material in which carbon atoms of graphite which is a three-dimensional structured carbon allotrope naturally present in the natural world are arranged in a hexagonal plane structure which is a two-dimensional sheet form. Carbon atoms of the graphene form a sp2 bond, and have a plane sheet form in a single atom thickness.
The graphene has significantly excellent electric conductivity and thermal conductivity, and physical properties such as excellent mechanical strength, flexibility, elasticity, quantized transparency depending on thickness, high specific surface area, and the like, may be explained by specific bonding structure of atoms present in the graphene. Three of four peripheral electrons of the carbons configuring the graphene form a sp2 hybrid orbital to have a sigma bond, and remaining one electron and the surrounding carbon atoms form a pi bond to provide a hexagonal two-dimensional structure. Therefore, the graphene has a band structure which is different from other carbon allotropes, and does not have a band gap to exhibit excellent electric conductivity; however, the graphene is a semi-metal material in which state density of electrons at the Fermi level is 0, and therefore, may easily change electrical properties depending on whether or not it is doped.
Accordingly, since the graphene may be variously applied to automobile, energy, aerospace, construction, and pharmaceutical fields as well as various electric electronic fields such as next-generation materials, capacitors, electromagnetic shielding materials, sensors, displays, and the like, which are replaceable for silicon electric electronic materials, research into a technology of utilizing the graphene in various fields has been largely conducted.
As a method for preparing the graphene, a scotch-tape method or a peel off method for exfoliating a graphene single layer from the graphite sheet using an adhesive tape, chemical vapor deposition, an epitaxial growth method by lamination on a silicon carbide substrate (SiC), thermal exfoliation of exfoliating the graphite by using heat, chemical reduction, or the like, has been researched.
Among them, the chemical reduction has advantages in that mass-production is possible, economic feasibility is provided, and various functional groups may be easily introduced into the graphene sheet. Meanwhile, in this method, reducing agents such as hydrazine, and the like, should be used for a deoxygenation reaction of graphene oxide, wherein most of these reducing agents are dangerous due to high corrosiveness, explosiveness, human toxicity, and the like, and the prepared graphene may include impurities, and the like, such that electric conductivity may be decreased. In addition, there is a possibility that each layer of the graphene after the reduction process is performed may be recombined, and it is difficult to control a size of the graphene, such that desired function of the graphene may not be effectively exerted.
Therefore, research into a method for modifying a graphene capable of obtaining the graphene having a desired crystallite size, even by more economical and low-risk processes, should be conducted.